1. Field of the Invention
The present invention relates a sample introduction device for introducing a sample into an analysis apparatus, such as liquid chromatograph. More particularly, the present invention relates to a total injection auto-sampler cleaning mechanism.
2. Description of Related Art
Total injection refers to a total amount of samples, taken from a sample bottle and metered by a sample needle, is completely injected from an injection port.
As for a sample introduction device capable of performing high precision metering regardless of the samples are micro samples or macro samples, it includes a metering pump and a multi-position valve. When a larger amount of samples is introduced, the samples are suctioned into a sample loop by switching the multi-position valve and performing the piston action back and forth by the metering pump (please refer to Japanese Patent Laid-Open Publication No. H10-170488).
Furthermore, if a larger amount of samples is introduced, the dead volume may increase occasionally. Therefore, a total injection liquid chromatograph has been proposed, in which the injection port is directly connected to a flow path switching valve without passing through any fitting pipe; thus, the dead volume and the retention volume of the flow path can be decreased (please refer to Japanese Patent Laid-Open Publication No. 2003-215118).
Furthermore, as for a total injection auto-sampler capable of injecting samples at a high metering precision even when a small amount of sample is introduced, an automatic sample introduction device with a function of automatically performing a sample pretreatment step has been proposed (please refer to Japanese Patent Laid-Open Publication No. 2006-242720).
Generally, a cleaning solution is supplied by a mechanism, including the pump of the metering portion or a syringe.
When a mechanism, for example, a pump or a syringe, is used to supply a liquid, in order to make the cleaning solution not flowing back during the suction and ejection process, a flow path switching valve is generally used to serve as a check valve. In this manner, as the cleaning solution cannot be supplied during the suction process, even if the amount of the supplied liquid is expected to increase, and time is only being consumed in the process of ejecting the liquid for the entire liquid-supply process.
Furthermore, when using a check valve, it is required to accurately stop the flow of the liquid in order to maintain the metering precision. However, in practice, there may exist a slight leakage of the liquid, and thus it is difficult to accurately stop the flow of the liquid.